Document JrX1n0v3kvwd3YNm8o4e25ke6

666 CHAPTER 25 1958 Guide units are not generally equipped with controls. Control systems for remote unite, and auxiliary controls for self-contained units, are covered in the general treatment of Controls, in Chapter 38. RATINGS OF UNIT AIR CONDITIONERS Two standards have been used for rating and testing of unit air con ditioners: (1) Standard. Method of Rating and Testing Air Conditioning Equipment,1 covering all types of air conditioning unite except the selfcontained type and (2) Standard Method of Rating and Testing SelfContained Air Conditioning Unite for Comfort Cooling2 covering the selfcontained type. (ASRE Standard Methods of Rating and Testing Air Conditioners, ASRE Standard 16-56, covers rating and testing of all types which operate non-frosting when cooling and dehumidifying at standard rating conditions.) The standard rating of a self-contained unit for the conditions specified in Table 1, includes all items which apply to the function of a unit as: (1) name of unit, (2) functions which unit performs, (3) data on cooling, (4) data on heating, (5) data on air flow, and (6) data on humidification. The standard rating conditions for unit air conditioners, other than the self-contained type, are identical with those in Table 1, except that entering wet-bulb temperature for cooling is expressed as 50 percent relative humidity (66.7 F wet-bulb) instead of 67 F wet-bulb temperature. In addition, the saturated suction refrigerant temperature for comfort cooling is specified at 40 F. This condition is omitted from Table 1 for self-contained unite because it is not separately controllable in the testing of a unit that includes the evaporator and condensing unit. APPLICATION OF UNITARY EQUIPMENT One of the chief advantages resulting from use of factory produced unite is the saving in installation and field assembly labor, a factor that should always be kept in mind when selecting-a location for these units. Because of their compactness, the tendency exists to put them in closets, storage rooms, and other inaccessible places, where installation is so difficult that much of this cost advantage is lost. Access panels are provided on unite for the proper servicing and main tenance of the equipment. Adequate outside clearance at these panels is essential. Wherever there is danger of freezing of coils or clogging with dirt, sufficient clearance should be available for replacing them without removing parte of the building. The outstanding source of difficulties in unitary systems is usually dirty filters. The characteristics of the light weight fans used are such that air volume drops off rapidly with increase in static resistance. Since changing of filters is an unpleasant duty likely to be neglected unless it can be done easily, the operator should be at the same level as the filters, rather than under them, when they are being removed. Variable-pitch motor pulleys are usually provided for adjustment of the air quantity. The fans and motors of most conditioners are selected for the usual range of external resistances commonly used with the specific size of conditioner. The larger conditioners are capable of serving larger areas and therefore require fan and motor capacity for the greater external duct resistances that may be imposed on such conditioners. Where varying sizes of coils are used within the same casing, it is very important that coil safing be carefully installed to prevent bypassing of unconditioned air. If coils are not equipped with individual casings* Unit Air Conditioners and Unit Air Coolers 667 Table 1. Standard Rating Basis fob Self-Contained Air Conditioning Units Functions All Cooling Heating Types of Unttb Item Rating Condition Description ; Value i All a Barometric Pressure 29.92 in. Hg. Water-Cooled, Air - Cooled and EvaporativelyCooled Con densers b c Unit Ambient and Air Entering Room--Air Inlet (1) Dry-Bulb (2) Wet-Bulb Ventilation Air Water-Cooled d 'Water Temperature Entering Condensers Unit e Water Temperature Leaving Unit .80 F 67 F See Note 75 F 95 F Air - Cooled and Evaporatively Cooled Con densers f 'g All Types Pro vided with h Heating Function Air Entering Outside Air hilet (1) Dry-Bulb (2) Wet-Bulb Unit Ambient and Total Air Entering Unit Heating Medium, Pressure or Temperature (1) Dry Saturated Steam (2) Water In (3) Water Out 95 F 75 F 70 F 16.7 lb per sq in. abs 180 F 160 F All Types i Unit Ambient Provided Humidifying with Hu j Total Air Entering Unit midifying (1) Dry-Bulb Function (2) Wet-Bulb Air ^ Circula tion All k Filters 70 F 70 F 53 F New and Clean 67 , nat*ng sh&U be based on both ventilation and recirculated room air entering at 80 F dry-bulb and '? wet-bulb temperature. (The Note as given in the code has been condensed in order to remove material not pertinent to this chapter). additional safing may be required on top to prevent short circuiting air down through the upper edges of the fins. In this same category is the need for careful installation of the various sections of sectionalized vuute, using a sealing compound if necessary to prevent air leakage into the fan section of the unit. Since the drain connection is usually made on the exit side of the coil, jt is important that the drain line be properly sealed. This seal should he at least twice as deep as the suction on the fan in inches of water, of ?!jeVen^ Shrglipg sounds, and to insure a positive seal against infiltration rttb8 ar^ mis!ure laden air. Drain pans should not be used to sup- Asth 6 co**s' hofess they are designed to hold this weight without sagging, ^s the movement of air draws the condensate or excess humidification ater toward the fan, drain connections are usually placed on the exit